Revolving Field Theory Research Articles

Analysis of a proposed connection for the two-winding single-phase self-excited induction generator operating at constant voltage and frequency

This paper introduces the steady-state and dynamic behaviors of a proposed connection for the two-winding single-phase self-excited induction generator (TWSPSEIG) equipped with an excitation capacitor and a compensation capacitor for operation at constant load voltage and frequency irrespective of the no-load or different load conditions. The performance equations at steady-state conditions are attained by applying loop impedance method via the exact equivalent circuit models of the TWSPSEIG based on the double revolving field theory. Keeping the values of the excitation capacitor and the compensation capacitor as unknowns, two second-order equations, for given values of generator parameters, prime mover speed, frequency and load impedance, are derived. These equations are solved using simple iterative method to calculate the optimum values of the two capacitors under the constraints that the load voltage and frequency are constant. The range of capacitor variations for variable load at variable prime mover speed is also calculated. The steady-state results are verified by developing the dynamic model of the proposed connection incorporating its nonlinearity behavior and various no-load and load conditions. The dynamic behavior of the proposed connection proves the capabilities of the proposed configuration and calculation method to maintain both the load voltage and frequency constants. A comparative study between the performances of the proposed connection and the traditional connection of the TWSPSEIG is presented to illustrate the merits of the proposed connection.

Development of a new control strategy based on two revolving field theory for single-phase VCVSI integrated to DC microgrid

This paper proposes a new control strategy of single-phase Voltage Controlled Voltage Source Inverter (VCVSI) based on Two Revolving Field Theory (TRFT) for integrating the single-phase static as well as dynamic ac loads to the DC Microgrid (DCMG). In the developed control scheme, the output ac voltage/current of the single-phase VCVSI has been decomposed into two counter rotating vectors, referred as Forward-Positive (FP) and Backward-Negative (BN) vectors, by using TRFT principle. The α-β components of the FP and BN rotating vectors have been obtained using the orthogonal transformation. The new control scheme, with dual controllers; one for the FP vectors and another for the BN vectors of the output ac voltage/current of the VCVSI, has been implemented into two rotating d-q synchronous reference frames, using a feed-forward and two feed-back control loops. The objective of the proposed controllers is to establish the VCVSI rated output ac voltage with low total harmonic, faster transient response after disturbances, and to ensure needed power flow from the microgrid to the single-phase loads. Simulations have been carried out to show the effectiveness of the developed control scheme along with the proposed DCMG in the islanded mode, under different operating conditions.

A single-phase induction motor operating as a self-excited induction generator

Abstract The purpose of the paper is the investigation of possibility of utilization of a single-phase induction machine, designed and normally operating as a single-phase capacitor induction motor, as a self-excited single-phase induction generator, which can be used to generate electrical energy from non-conventional energy sources. The paper presents dq model of the self-excited single-phase induction generator for dynamic characteristics simulation and steady-state model based on double revolving field theory with two phase symmetrical components - a forward and backward revolving field for performance of the generator under resistive load. Excitation and load characteristics obtained by simulation showed considerable influence of method of capacitor configuration in the load stator winding on terminal voltage, current and output power of the generator under load. An specific construction of the stator windings together with capacitor requirements to obtain nominal output power at desired self-regulating terminal voltage over the operating range will be the aim of further research.

등가회로법에 의한 커패시터 구동 단상 유도전동기의 특성해석

This paper proposes a straightforward method of analyzing the operation characteristics for the capacitor run single-phase induction motor from the traditional equivalent circuit based on the revolving field theory. The proposed method consists of five procedures as follows: mechanical loss segregation, iron loss segregation and calculation of the equivalent circuit parameters, recalculation of parameters of the main winding side, calculation of the auxiliary winding magnetizing reactance and effective turn ratio, and analyzing the operation characteristics for this motor. When the characteristics are analyzed, the segregated mechanical and iron losses are considered as a loss resistance across input terminals of the equivalent circuit for the analysis. The validity of the proposed method is verified from the comparison between the computed results and the experimental ones for the operation characteristics.

Generalised approach to the analysis of asymmetrical three-phase induction motors

The growing interest in single-winding multi-speed induction motors, in which some unbalance of the windings has been in many cases inevitable, and the use of normal fractional slot windings, in which some unbalance has to be accepted, makes it an important task to devise a general method for predicting the performance of induction motors with asymmetrical stator windings. The paper presents a new original method for analysing such windings. The analysis is based on revolving-field theory and three-phase symmetrical-component theory. The analysis starts from inside the machine using the current sheet approach, taking into account the harmonics effect, and ends up with viewing the machine from outside as an electrical network having easy to calculate parameters. The analysis is supported by experimental results obtained from a test model built for this purpose.

Analysis of wind driven grid connected induction generators under unbalanced grid conditions

A wind driven induction generator feeding power to the grid has been analyzed under the abnormal condition of unbalanced grid voltages. Using the symmetrical component and double revolving field theory, appropriate equivalent circuits and model equations have been derived for the generating mode with suitable realistic modifications. It is emphasized that the active and reactive power components and their directions for both positive and negative sequence systems need to be properly identified in order to obtain the cumulative response of the generator under different wind power conditions. In view of the fact that the reactive power is drawn from the grid while the active power is fed into the grid, the extent of variations in power fed to the grid and the reactive VAr due to unbalanced grid voltages for different wind power conditions need to be estimated to provide guidelines in the design and operation of the wind energy conversion system. Both experimental and theoretical results for a 3.7 kW laboratory model have also been presented, to validate the theoretical formulations, extendable to large units. Extensive data have been presented and discussed for a 55 kW unit installed in site. >

Analysis of wind driven grid connected induction generators under unbalanced grid conditions

A wind driven induction generator feeding power to the grid has been analyzed under the abnormal condition of unbalanced grid voltages. Using the symmetrical component and double revolving field theory, appropriate equivalent circuits and model equations have been derived for the generating mode with suitable realistic modifications. It is emphasized that the active and reactive power components and their directions for both positive and negative sequence systems need to be properly identified in order to obtain the cumulative response of the generator under different wind power conditions. In view of the fact that the reactive power is drawn from the grid while the active power is fed into the grid, the extent of variations in power fed to the grid and the reactive VAr due to unbalanced grid voltages for different wind power conditions need to be estimated to provide guidelines in the design and operation of the wind energy conversion system. Both experimental and theoretical results for a 3.7 kW laboratory model have also been presented, to validate the theoretical formulations, extendable to large units. Extensive data have been presented and discussed for a 55 kW unit installed in site. >

Experimental determination of the forward and backward-field torque in shaded-pole motors

An experimental method for determining the forward- and backward-field torque and the amplitude of a pulsating torque at twice the line frequency in shaded-pole motors is developed on the basis of revolving-field theory. These parameters are determined from the induced voltage in a measured winding by segregating a forward and backward fundamental component using a spectrum analyzer. This torque-measuring method has been tested for a shaded-pole motor with one shading coil, and a shaded-pole motor with two shading coils per pole. The forward-field torque minus the backward-field torque, as measured by the measuring winding, agreed with that measured by a Prony-brake torque meter with sufficient accuracy. The amplitude of the pulsating torque also agreed approximately with that measured with an accelerometer. Each torque can be determined more precisely in this experimental technique than in existing calculation techniques.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Experimental Determination of the Forward and Backward-Field Torque in Shaded-Pole Motors

An experimental method for determining the forward- and backward-field torque and the amplitude of a pulsating torque at twice the line frequency in shaded-pole motors is developed on the basis of revolving-field theory. These parameters are determined from the induced voltage in a measured winding by segregating a forward and backward fundamental component using a spectrum analyzer. This torque-measuring method has been tested for a shaded-pole motor with one shading coil, and a shaded-pole motor with two shading coils per pole. The forward-field torque minus the backward-field torque, as measured by the measuring winding, agreed with that measured by a Prony-brake torque meter with sufficient accuracy. The amplitude of the pulsating torque also agreed approximately with that measured with an accelerometer. Each torque can be determined more precisely in this experimental technique than in existing calculation techniques. >

Revolving-Field Analysis of a Shaded-Pole Motor

The revolving-field theory as applied to singlephase induction motors is extended to develop a concise, yet comprehensive, theory for shaded-pole motors with single shading coil. The analysis can, however, be easily extended for motors with multiple shading coils. The novel features of this development are that it provides means to properly account for the magnetic saturation, space harmonics and the core loss. The analysis is based upon the concept that a winding can be simulated by a pair of mutually perpendicular windings. Based upon this concept and the revolving-field theory, an equivalent circuit for a shaded-pole motor is proposed. Performance equations are then presented and a step by step procedure is outlined to effectively utilize these equations. The accuracy of the development was confirmed by actual measurements on shaded pole motors with various horsepower ratings. To show that the present development yields better correlation, comparisons between actual test results and computed data using the present model, as well as other existing models are also given.

REVOLVING-FIELD ANALYSIS OF TWO-SPEED SHUNTED CAPACITOR MOTORS WITH NONQUADRATURE WINDINGS

ABSTRACT The main purpose of this paper is to extend the well-known revolving-field theory for the general development of the so-called analysis equations to predict the performance of two-speed shunted capacitor motors with arbitrary arrangements of their primary windings. It has been found that sometimes by arranging the auxiliary winding at an unconventional location, the motor efficiency can be considerably improved especially at low-speed setting. The accuracy of the present mathematical development has been confirmed by actual measurements on such motors with windings both in quadrature and nonquadrature

Revolving-Field Analysis of T- and L-Connected Capacitor Motors with Arbitrarily Displaced Windings

Performance equations on T- and L-connected tapped-winding capacitor motors with both the extra-main and the auxiliary windings arranged arbitrarily in space from the main winding are presented in this paper, using the revolving-field theory. Also shown is the fact that these general equations can be employed to yield performance on conventional T- and L-connected capacitor motors. By displacing the windings at locations other than conventional, it has been found that the motor effeciency increases considerably for both high and low-speed operations as well as the manufacturing cost goes down. The variations in the net torque developed and the efficiency as a result of changing the locations of the extra- main and/or the auxiliary winding are shown for the purposes of illustration.

Revolving-field analysis of asymmetric 3-phase machines and its extension to single- and two-phase machines

The revolving-field theory as applied to single-phase induction motors is extended to develop a concise yet comprehensive theory for asymmetric three-phase induction motors. Each phase is represented by its equivalent circuit, not only to allow for uneven direct transformer interactions, due to asymmetric locations of phase windings, but also to account for the different number of turns, wire size, winding factor etc. each phase may have. The accuracy of the theory was confirmed by actual measurements on symmetric and asymmetric three-phase induction motors. Computed and test data on some motors are included for illustration. It is also shown that the general three-phase development can be easily applied to determine the behaviour of two- and single-phase induction machines, a useful feature for unified computer-aided design, by eliminating one and two phase windings, respectively. Not only the procedural details for determining the performance of single- and two-phase induction motors are given, but comparisons of numerical and test results on some output entities are included as well. Though the comparisons among theoretical and test results are made on fractional horsepower motors, the types being built at Universal Electric, the author is certain that the development presented here is equally applicable to all sizes of induction motors.

REVOLVING-FIELD ANALYSIS OF CAPACITOR MOTORS WITH NONQUADRATURE WINDINGS

ABSTRACT Equations to determine the performance of a single-phase induction motor, especially a capacitor motor, with non-quadrature windings are presented, using the revolving-field theory. Since the capacitor motor represents a very special case in the family of single-phase induction motor, emphasis is thereby placed upon its performance calculations. A procedure arranged in very systematic steps to help analyze an induction motor is also included. In order to demonstrate the influence of winding displacement, the results on a typical permanent-split capacitor motor are also tabulated. To verify the accuracy of these equations, the theoretical results when compared with those obtained from the cross-field development for such motors showed an exact agreement.

A Method of Finding Equalizer Section for D-C Armature Winding [includes discussion

This paper presents a new theorem for equalizer of d-c machinery and a simple method of estimating its required size, for d-c lap windings under some assumed type of unbalance, by an equation derived from the conventional revolving field theory of polyphase induction motors. It is shown that only a very small conductor section will be sufficient for ordinary anticipated type of unbalance. In reaching the equation, power limits of various types of d-c armature windings as a consequence of the permissible voltage between adjacent commutator bars are discussed.

MONECA - A New Network Calculator for Motor Performance Calculations [includes discussion

Performance calculations on single-phase induction motors require two to four times as much time as comparable calculations on polyphase motors. This paper describes MONECA, a new calculator developed especially for these calculations. It is based upon a new revolving-field equivalent circuit, but can be readily reconnected for many other different circuits. It has shortened the time for many present calculations, made practicable many calculations that were formerly too time-consuming, and has given its users a clearer concept of the revolving-field theory. It appears to have an almost unlimited number of future applications.

Steady-State Equivalent Circuits of Synchronous and Induction Machines

Equivalent circuits are developed for the various types of salient-pole synchronous and asymmetrical induction machines, expressed along the physical direct and quadrature axes (cross-field theory). The torques again are found by a direct measurement of power. The networks of all types of machines are found as special cases of that of the ``primitive'' machine. All equivalent circuits along the physical axes are derivable from those along the hypothetical symmetrical component axes (revolving-field theory) by a real transformation. Although the latter types of networks have already been published previously, they are reproduced here for comparison with the new networks and for a unified tensorial treatment of rotating machines and their equivalent circuits.

Transactions section: Preprint of corresponding pages from the current annual AIEE transactions volume

THE tapped-winding capacitor motor is used quite commonly to obtain a two-speed fan motor with a comparatively simple switching arrangement. With the open-end type of connection as shown in Figure 1, the high-speed connection gives a normal capacitor motor, and its performance under any load may be determined by calculation with the formulas of either the revolving-field theory or the cross-field theory. When a control winding is added to the already complicated capacitor motor circuits, the analysis by the usual methods becomes even more difficult, and the calculation more involved and tedious than ever. In the following discussion a method is presented for calculating the low-speed performance. This method while not absolutely rigorous, should give results well within the limits of variation of individual motors of the same design.

The Apparent-Impedance Method of Calculating Single-Phase-Motor Performance

In the past several years there have been offered a number of calculation methods to be used in connection with predetermining the performance of single- phase induction motors. While such methods are usually based upon either the cross field or the revolving field theory, they differ from each other according to individual preferences. In the present paper there is proposed a method which seems to be convenient and simple, and which, because of symmetry, involves a minimum of charts in carrying out the necessary calculations. The method is proposed because it has been used in one design department for a number of years and found to be very satisfactory as a practical method.

The apparent-impedance method of calculating single-phase-motor performance

In the past several years there have been offered a number of calculation methods to be used in connection with predetermining the performance of single-phase induction motors. While such methods are usually based upon either the cross field or the revolving field theory, they differ from each other according to individual preferences. In the present paper there is proposed a method which seems to be convenient and simple, and which, because of symmetry, involves a minimum of charts in carrying out the necessary calculations. The method is proposed because it has been used in one design department for a number of years and found to be very satisfactory as a practical method.